Disabling basic authentication

["Florian Niedoba" <mail@xxxxxxxxxxxxxxxxxx>]

Hi,

This is about disabling basic authentication.
We currently use the following scenario:
We are using mod_auth_sspi to authenticate users via Single Sign On. This works fine.
Some of our users are not on the Active Directory.
What we want for them is: They hit the URL which protected by the mod_auth_sspi, it fails and they are forwarded to a different url with a form based login (401 redirects them).
What happens currently: They are prompted with a basic authenitication pop-up for username and password, but they don't have a valid AD user so authentication fails. Now they are forwarded to the other url with the form based login.
So everything works fine, except that we want to get rid of the basic auth pop-up.
Is there any chance to suppress it? Any ideas? I think it is actually done by the browser, is there a way to modify a header or something to pretend the apache can not handle basic authentication?
About our env: AD as authentication source, all users use IE, we have full controll over their IE settings, we are using  apache 2.0.59

Thanks, Florian